<!DOCTYPE html>
<html lang="en">
	<head>
		<meta charset="utf-8">
		<title>my title</title>
		<style type="text/css">
			#head{
				width: 80%;height: 100px;background: #f00;
				margin: 0px auto;
			}
			#cnt{
				width:80%;height: 500px;background: #00f;
				margin: 0px auto;
			}
			#cnt #c-left{
				width: 20%;height: 200px;background: rgb(41, 233, 66);float: left;
			}
			#cnt #c-middle{
				width: 50%;height: 200px;background: rgb(153,56,63);float: left;
				margin-left: 20px;margin-right: 30px;
			}
			#cnt #c-right{
				width: 20%;height: 200px;background: rgb(238, 234, 11);float: left;
			}
		</style>
	</head>
	<body>
		<div id="head"></div>
		<div id="cnt">
			<div id="c-left">1</div>
			<div id="c-middle">2</div>
			<div id="c-right">3</div>
		</div>
	</body>
</html>